Virioplankton was first proposed by American scholars wommack et al. (1999), when it was believed that virioplankton was a virus floating in a body of water. It is now generally believed that planktonic viruses are a general term for various groups of viruses that are hosted by various aquatic organisms or exist in water bodies, including animal viruses, plant viruses and microbial viruses with different taxonomic statuses (Zhang Qiya, Gui Jianfang. 2008）。 The discovery of the planktonic virus is considered "a major discovery that may affect the direction of modern biology in marine geography and limnology" (fuhrman. 1999）。 Viruses are the most abundant organisms in water, with a content of about 1 billion viruses per liter of water, but the ecological significance of planktonic viruses has only been recognized in recent years, and the research has progressed rapidly and attracted widespread attention (suttle. 2005）。
A large number of research results confirm that planktonic virus is the most abundant active ingredient in the aquatic microbial community, which regulates the species diversity, population distribution and community structure of aquatic microorganisms by cracking the dominant populations in the aquatic microbial communities, affecting the flow of carbon and nutrients, and thus affecting the biodetection cycle and global climate (bettarel, sime-ngando & amblard et al. 2004）。 In addition, planktonic viruses can also mediate gene transfer between microorganisms in aquatic ecosystems by transduction, transformation and lysis conversion, affecting the diversity of aquatic microbial communities at the genetic level (weinbaure & rassoulzadegan. 2004）。 For example, studies have shown that 10-50% of planktonic bacterial deaths are caused by planktonic viruses, and the lysis of viruses promotes the flow of bacteria to soluble organic confluence pools, thus affecting the microbial cycle (fuhrman. 1999), it can be seen that planktonic viruses have an important impact on the aquatic environment and even the entire ecosystem.
At present, the research on aquatic viruses in the domestic academic circles mainly focuses on pathogenic viruses, such as leukoplakia syndrome virus (He Jianguo, Weng Shaoping, Lü Ling, et al. 2005) and frog iridescent virus (zhang, zhao & xiao et al. 2006), aquatic reovirus (Fang Qin, shah, liang, et al. 2005), etc.; while there are relatively few studies on planktonic viruses that have an absolute advantage in water bodies, but in recent years there have been some reports on freshwater lakes, wetlands, and inshore and cultured water bodies. In terms of freshwater lakes, experts from the Institute of Hydrobiology of the Chinese Academy of Sciences have carried out a more systematic study of planktonic viruses based on the shallow water-type lake - East Lake, located in the middle and lower reaches of the Yangtze River and in Wuhan City. The abundance of phytoplanktonic virus in East Lake was found to be about 109/ml, and the ultrastructure showed the presence of phages, algae phagosomes and different groups of planktonic viruses in the water bodies of East Lake, including nontailed virus, myoviridae and long-tail virus (Liu Yanming, Zhang Qiya, Yuan Xiuping. 2005;Yuan Xiuping, Liu Yanming, Zhang Qiya. At the same time, the genome size of East Lake planktonic virus was determined by pulsed field electrophoresis technology, and the genome size of East Lake planktonic virus was found to be between 15 and 300 kb, most of which was concentrated in 20-60 kb, and the East Lake plankton virus was divided into five taxa according to the characteristics of electrophoresis. Bioinformatics analysis speculates that The East Lake virus is mainly a eukaryotic algae virus, of which algae-eating bodies and some algal viruses have attracted much attention because of their potential to control blooms and red tides (Liu Yanming, Zhang Qiya. 2005）。 In terms of wetland water bodies, Sun Xiaolei et al. (2009) conducted a large-scale study on the distribution of planktonic viruses in 15 wetland water bodies with different nutrient levels in Hubei Province. The results showed that the abundance of planktonic virus was not only significantly correlated with the number of live bacteria and chlorophyll a concentration, but also with cod and water temperature, which proved that organic matter concentration and water temperature were important factors that determined the spatial and temporal distribution of planktonic viruses in freshwater wetlands, respectively. In terms of coastal waters, Liang Yantao et al. (2008) investigated the abundance of planktonic viruses in the coastal waters of Qingdao using fluorescence microscopy technology, and studied the seasonal changes of planktonic viruses and the correlation between floating virus abundance and environmental factors. The results showed that the summer phytoplanktonic virus abundance in the water areas was significantly higher than that in winter, and the correlation analysis showed that the summer phytoplanktonic virus abundance was only significantly positively correlated with chlorophyll a, while the winter phytoplanktonic virus abundance was significantly positively correlated with water temperature, and there was a significant negative correlation between chlorophyll a, salinity, turbidity and dissolved oxygen. In terms of aquaculture water bodies, Jiang Bei et al. (2008) used fluorescent microscopy to monitor and analyze the abundance of planktonic viruses in four areas near Dalian and the corresponding sea areas, and found that there were significant differences in the temporal and spatial distribution of planktonic viruses in the ponds of ginseng culture, and the average abundance reached a peak in mid-August2. 54 × 1010 pcs/l, with the lowest average abundance of planktonic virus in late July was 1. 43 × 109/l, and the abundance of planktonic viruses in the water body of the ginseng culture pond is closely related to the location of the sea area where the culture pond is located and the density of the culture pond.
Different from the current situation of domestic investigation and research, the international research hotspots mainly include the genetic diversity of planktonic viruses and the distribution of planktonic viruses in extreme water environments. Marjolijn et al. (2008) used fluorescence electron microscopy and pulse field electrophoresis to study the abundance and genetic diversity of the phytoplanktonic virus of the nutrient-rich loosdrecht lake in a shallow dutch shoal, and found that the abundance of the phytoplanktonic virus in the lake was 5.5 × 107-1.3×108/ml, the genome of the virus was between 30 and 200 kb, and the fluctuations of the planktonic virus were consistent with the fluctuations of bacteria and phytoplankton. The research team of wommack, the founder of the field of floating viruses, has spent more than a decade conducting in-depth research on the planktonic virus in the Chesapeake Bay in the United States. They used pulsed field electrophoresis techniques (wommack, ravel & chun et al. 1999), molecular hybridization techniques (wommack, ravel & hill et al. 1999), metagenomics technology (bench, hanson & williamson et al. 2007; wommack, bhavsa & ravel. 2008), rapd-pcr technology (winget & wommack. 2008) Conducted a systematic study of the genetic diversity of chesapeake bay planktonic virus. It was confirmed that the genome of chesapeake bay planktonic virus was between 50 and 300 kb, and the metagenomic analysis of dsdna floating virus found that unknown sequences and non-homologous sequences accounted for 31% and 30%, respectively, indicating that dsdna virus occupies a major position in the bay; dna probe molecular hybridization technology can detect the sensitivity of a single virus to reach 1/1000 of the total floating virus abundance. Veronica et al. (2007) studied the abundance, decay and diversity of planktonic viruses in the deep water area of the North Atlantic, and found that with the increase of water depth, the abundance of planktonic viruses decreased significantly, and the abundance of planktonic viruses was about 4.0 ×105/ml at water depth of 2400 m, while the water depth dropped to 0.3×105/ml at 2750 m.
In summary, the above-mentioned studies on the abundance, spatio-temporal distribution, seasonal fluctuations, impact factors and genetic diversity of planktonic viruses have laid a good foundation for elucidating the effects and status of planktonic viruses in the corresponding water ecosystems.
Where is the end of life?
For a long time, big fish eat small fish, small fish eat shrimp, and shrimp eat mud is the crudest understanding of the food chain of water bodies. Who eats the bacteria? Who do bacteria eat? Who will crack the algae? Viruses can lyse bacteria and algae, is the virus the terminator? Combined with the current large number of vibrio leeches used in the aquatic animal protection industry, what is the risk?
Perhaps, the virus is just one part of the food chain. Life goes on and on, who is the Terminator?
( Aquatic Animal Health Assessment)